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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2011 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: ThreadParkingLot.html 689 2013-06-28 19:22:16Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.dellroad.stuff.java;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.util.Collections;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.util.HashSet;<a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.util.Set;<a name="line.12"></a>
<span class="sourceLineNo">013</span><a name="line.13"></a>
<span class="sourceLineNo">014</span>/**<a name="line.14"></a>
<span class="sourceLineNo">015</span> * A place for threads to be parked and unparked.<a name="line.15"></a>
<span class="sourceLineNo">016</span> *<a name="line.16"></a>
<span class="sourceLineNo">017</span> * @since 1.0.102<a name="line.17"></a>
<span class="sourceLineNo">018</span> */<a name="line.18"></a>
<span class="sourceLineNo">019</span>public class ThreadParkingLot {<a name="line.19"></a>
<span class="sourceLineNo">020</span><a name="line.20"></a>
<span class="sourceLineNo">021</span>    private final HashSet&lt;Thread&gt; parkedThreads = new HashSet&lt;Thread&gt;();<a name="line.21"></a>
<span class="sourceLineNo">022</span><a name="line.22"></a>
<span class="sourceLineNo">023</span>    /**<a name="line.23"></a>
<span class="sourceLineNo">024</span>     * Park the current thread on this instance. Execution will halt until {@link #unpark unpark()} is invoked<a name="line.24"></a>
<span class="sourceLineNo">025</span>     * by some other thread with the current thread as the parameter, the given non-zero timeout expires, or<a name="line.25"></a>
<span class="sourceLineNo">026</span>     * the current thread is interrupted.<a name="line.26"></a>
<span class="sourceLineNo">027</span>     *<a name="line.27"></a>
<span class="sourceLineNo">028</span>     * @param timeout maximum time to stay parked, or zero to park indefinitely<a name="line.28"></a>
<span class="sourceLineNo">029</span>     * @return {@code true} if the thread was unparked by another thread, {@code false} if the timeout expired<a name="line.29"></a>
<span class="sourceLineNo">030</span>     * @throws IllegalArgumentException if {@code timeout} is negative<a name="line.30"></a>
<span class="sourceLineNo">031</span>     * @throws InterruptedException if the current thread is interrupted<a name="line.31"></a>
<span class="sourceLineNo">032</span>     */<a name="line.32"></a>
<span class="sourceLineNo">033</span>    public synchronized boolean park(long timeout) throws InterruptedException {<a name="line.33"></a>
<span class="sourceLineNo">034</span>        final Thread thread = Thread.currentThread();<a name="line.34"></a>
<span class="sourceLineNo">035</span>        this.parkedThreads.add(thread);<a name="line.35"></a>
<span class="sourceLineNo">036</span>        try {<a name="line.36"></a>
<span class="sourceLineNo">037</span>            return TimedWait.wait(this, timeout, new Predicate() {<a name="line.37"></a>
<span class="sourceLineNo">038</span>                @Override<a name="line.38"></a>
<span class="sourceLineNo">039</span>                public boolean test() {<a name="line.39"></a>
<span class="sourceLineNo">040</span>                    return !ThreadParkingLot.this.parkedThreads.contains(thread);<a name="line.40"></a>
<span class="sourceLineNo">041</span>                }<a name="line.41"></a>
<span class="sourceLineNo">042</span>            });<a name="line.42"></a>
<span class="sourceLineNo">043</span>        } finally {<a name="line.43"></a>
<span class="sourceLineNo">044</span>            this.parkedThreads.remove(thread);<a name="line.44"></a>
<span class="sourceLineNo">045</span>        }<a name="line.45"></a>
<span class="sourceLineNo">046</span>    }<a name="line.46"></a>
<span class="sourceLineNo">047</span><a name="line.47"></a>
<span class="sourceLineNo">048</span>    /**<a name="line.48"></a>
<span class="sourceLineNo">049</span>     * Unpark a thread.<a name="line.49"></a>
<span class="sourceLineNo">050</span>     *<a name="line.50"></a>
<span class="sourceLineNo">051</span>     * @param thread the thread to unpark<a name="line.51"></a>
<span class="sourceLineNo">052</span>     * @return {@code true} if {@code thread} was successfully unparked, {@code false} if {@code thread}<a name="line.52"></a>
<span class="sourceLineNo">053</span>     *  is not parked on this instance<a name="line.53"></a>
<span class="sourceLineNo">054</span>     */<a name="line.54"></a>
<span class="sourceLineNo">055</span>    public synchronized boolean unpark(Thread thread) {<a name="line.55"></a>
<span class="sourceLineNo">056</span>        boolean wasParked = this.parkedThreads.remove(thread);<a name="line.56"></a>
<span class="sourceLineNo">057</span>        if (wasParked)<a name="line.57"></a>
<span class="sourceLineNo">058</span>            this.notifyAll();<a name="line.58"></a>
<span class="sourceLineNo">059</span>        return wasParked;<a name="line.59"></a>
<span class="sourceLineNo">060</span>    }<a name="line.60"></a>
<span class="sourceLineNo">061</span><a name="line.61"></a>
<span class="sourceLineNo">062</span>    /**<a name="line.62"></a>
<span class="sourceLineNo">063</span>     * Determine if the given thread is currently parked on this instance.<a name="line.63"></a>
<span class="sourceLineNo">064</span>     * Obviously, things can change so this only gives an answer at the point in time invoked.<a name="line.64"></a>
<span class="sourceLineNo">065</span>     *<a name="line.65"></a>
<span class="sourceLineNo">066</span>     * @param thread the thread in question<a name="line.66"></a>
<span class="sourceLineNo">067</span>     * @return {@code true} if {@code thread} is currently parked on this instance, {@code false} otherwise<a name="line.67"></a>
<span class="sourceLineNo">068</span>     */<a name="line.68"></a>
<span class="sourceLineNo">069</span>    public synchronized boolean isParked(Thread thread) {<a name="line.69"></a>
<span class="sourceLineNo">070</span>        return this.parkedThreads.contains(thread);<a name="line.70"></a>
<span class="sourceLineNo">071</span>    }<a name="line.71"></a>
<span class="sourceLineNo">072</span><a name="line.72"></a>
<span class="sourceLineNo">073</span>    /**<a name="line.73"></a>
<span class="sourceLineNo">074</span>     * Get all of the threads parked on this instance.<a name="line.74"></a>
<span class="sourceLineNo">075</span>     * Obviously, things can change so this only gives an snapshot at the point in time invoked.<a name="line.75"></a>
<span class="sourceLineNo">076</span>     *<a name="line.76"></a>
<span class="sourceLineNo">077</span>     * @return an unmodifiable {@link Set} containing a snapshot of all threads currently parked on this instance<a name="line.77"></a>
<span class="sourceLineNo">078</span>     */<a name="line.78"></a>
<span class="sourceLineNo">079</span>    public synchronized Set&lt;Thread&gt; getParkedThreads() {<a name="line.79"></a>
<span class="sourceLineNo">080</span>        return Collections.unmodifiableSet(new HashSet&lt;Thread&gt;(this.parkedThreads));<a name="line.80"></a>
<span class="sourceLineNo">081</span>    }<a name="line.81"></a>
<span class="sourceLineNo">082</span>}<a name="line.82"></a>
<span class="sourceLineNo">083</span><a name="line.83"></a>




























































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